JP2560252B2 - Silicon nitride fine powder and method for producing the same - Google Patents

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a high strength, high precision, wear resistant, corrosion resistant silicon nitride sintered material used as a machine part in the fields of semiconductor manufacturing machines, chemical plants, non-ferrous metal manufacturing machines, welding robots and the like. The present invention relates to a desirable silicon nitride fine powder as a starting material for a body and a method for producing the same.

[0002]

2. Description of the Related Art As a silicon nitride powder for sintering, there are conditions such as (1) high α ratio, (2) fine particles, (3) high purity, (4) spherical shape, and (5) narrow particle size distribution. Has been needed. For this reason,
High purity, α ratio of 90% or more, and average particle size of 0.5 to 0.5.
Silicon nitride as fine as 8 microns is commercially available.
This powder is referred to as submicron powder because most particles are 1 micron or less.

An oxide was added to this powder as a sintering aid,
When heated to 1700 ° C. or higher in nitrogen, a high density sintered body can be manufactured. Densification is achieved by liquid phase sintering in which silicon nitride diffuses in a liquid phase containing a sintering aid. Since β-type is stable at high temperature, α-particles are dissolved and precipitated as β-particles as sintering proceeds. In this process, the phase transition from α to β progresses.

After cooling, the liquid phase solidifies into glass, so that the sintered body has a structure in which a small amount of β particles are bonded to the glass phase. The particles grow in a columnar shape with the phase transition from α to β. Most of the structure of this sintered body is small β particles, and a small number of columnar grown β particles are dispersed into a composite structure. This structure is the same as the wicker reinforced ceramics. Since the columnar particles resist the progress of cracks, the sintered body has high toughness and
It has high strength. This is the reason why the high α ratio was an essential condition as a starting material.

One of the inventors of the present invention is already in Japanese Patent Application No. 1-771.
In No. 77, it was shown that a high α ratio is not an essential condition, and that a powder with a high β ratio will have high sinterability if it is a submicron powder. Further, when grain growth nuclei were added, columnar grains grew and a composite structure developed, so that a high-strength / high-toughness sintered body was obtained. In the subsequent research, the particle size distribution in which columnar particles can grow was clarified, and Japanese Patent Application No. 3-245868.
And Japanese Patent Application No. 3-338844.

[0006]

There are many commercially available powders having a submicron and a high α ratio. The grain growth behavior during sintering of powders with a high α ratio is closely linked to the phase transition. This phase transition rapidly progresses in a certain temperature range and cannot be controlled. Therefore, the reproducibility of the structure is low, the strength distribution of the sintered body is wide, and the reliability as a material is low.

Previous studies have revealed that columnar grains grow from powders with a high β ratio without the involvement of phase transition. However, the average particle diameter of the powder provided in the conventional research is large, and a high temperature of 1850 ° C. or higher is required to manufacture a high density sintered body having a relative density of 98% or more. In addition, the above-mentioned proposal (Japanese Patent Application No. 3-245868, Japanese Patent Application No. 3-33)
It has been revealed that columnar grains grow from large grains without introducing nuclei when a powder having a particle size distribution defined in (No. 8844) is sintered at high temperature (J. Am. Ceram.
Soc. 76, 1892 (1993)). Therefore,
Even the conventional powder having a high β ratio is not sufficient for controlling the structure.

From these results, it is impossible to reproducibly control the texture of any powder having a high α ratio and a high β ratio simply by using a submicron powder. Therefore, a raw material powder that does not develop columnar particles during sintering and gives a fine and uniform structure is required.
If large particles outside the particle size distribution are added to the powder as cores, columnar particles should develop only from the cores. The size and shape of the columnar particles are controlled by not only the sintering temperature and the type of sintering aid, but also the number and size of nuclei. Therefore, the particle size and particle size distribution of the raw material powder that provides the matrix (matrix) are the most important for controlling the composite structure. Therefore, it is necessary to remove particles larger than 0.5 micron that act as nuclei from the submicron powder to provide a powder having a narrow particle size distribution.

In order to control the tissue expression with good reproducibility, it is necessary to use a raw material capable of producing a sintered body having a fine and uniform grain size as a matrix (matrix) as described above.

In order to meet such a problem, an object of the present invention is to provide a raw material fine powder for a silicon nitride sintered body, which has a finer particle size distribution and a wider specific surface area than ever before.

[0011]

Means for Solving the Problems As means for solving the above problems, the present invention has an average particle diameter measured by a laser scattering method within a range of 0.1 to 0.35 micron, and a particle diameter of The content of particles of 0.5 micron or more is 15% by volume
In the following, the content of particles having a particle size of 1.0 micron or more is 3% by volume or less, and the specific surface area is 15 to 50 m ² /
It is used for crystalline silicon nitride fine powder characterized by being in the range of g.

The manufacturing method is as follows. Disperse the silicon nitride powder in a solvent by wet pulverizing with a ball mill,
It is characterized in that after forming a silicon nitride powder slurry, coarse particles are removed by wet sedimentation classification to produce fine particles having a narrow particle size distribution.

Still another aspect of the present invention is that the average particle size measured by a laser scattering method is more than 0.5 micron and 1.5 micron or less, and the particles within the range are 70% by volume or more of the whole, and Specific surface area of 5 m ² / g or less, β phase content of 80
The gist of the silicon nitride fine powder is characterized by mixing 0.1% to 5% by weight of the above silicon nitride fine powder with silicon nitride powder in an amount of at least wt%.

[0014]

The present invention will be described in more detail below.

Commercially available powders for sintering raw materials are submicron, with a particle size distribution in the range of 0.1 to 3 microns, with most particles less than 1 micron. To remove particles larger than 0.5 micron from this powder, a sedimentation method that ensures the removal of large particles is desirable.
Therefore, a commercially available powder is dispersed in a dispersant solution in which a deflocculating agent is dissolved, and a ball mill is used to pulverize and uniformly disperse the powder, and then large particles are removed by a sedimentation method. Although there are various sedimentation methods, the centrifugal sedimentation method, which can be performed in a short time, is the simplest. However, it is not limited to the sedimentation method as long as it is a separation method in which fine particles and large particles are separated by 0.5 micron within a submicron range and fine particles do not include larger particles.

The particle size distribution is measured by dispersing a small amount of powder in water and using a laser scattering method, a sedimentation method or an X-ray transmission method. Direct measurement is performed with a transmission electron microscope or a scanning electron microscope. Most commonly, the laser scattering method is used, which takes advantage of the fact that the scattering of laser depends on the size of particles. However, the measured particle size distribution is not the true size distribution of the particles. This is because in many cases, there are secondary particles in which fine particles are strongly bound in the process of powder synthesis, and their size is reflected in the particle size distribution. During the sintering process, the large particles absorb the surrounding fine particles and grow into columns. Since the secondary particles are also strongly bound to each other, the sintering proceeds at a temperature lower than that of the matrix, and the secondary particles act as nuclei like large particles. However, since the secondary particles generated during the pulverization and dispersion operations are weakly bonded, they are dispersed during sintering and do not act as nuclei.

In order to clarify the difference between the secondary particles, it has been found that the measurement of the particle size distribution is not sufficient, and the measurement of the specific surface area using the nitrogen adsorption method must be used together.
If the secondary particles have a strong bond, the specific surface area is evaluated to be small like the large particles, but the particles having a weak bond are evaluated as the specific surface area of the primary particles because nitrogen is adsorbed between the particles.
The specific surface area of submicron particles is about 8 to 12 m ² / g, and most of the particles are 0.1% in the powder with large particles removed.
15 to 50 m ² / g in the range of up to 0.5 micron
Becomes

As described above, the method of pulverizing and dispersing with a ball mill and then removing the large powder by the sedimentation method is effective for adjusting the powder having a fine and uniform particle size. Then, the particle size distribution and the specific surface area are measured together by the laser scattering method to confirm that the desired powder is obtained.

The commercially available submicron particles have a particle size distribution measured by a laser scattering method as shown in Comparative Example 3 in FIG. Average particle size is 50% volume% (same as weight%)
In the figure, it is 0.51 micron. The submicron powder contains about 50% by volume of the desired particles of 0.5 micron or less. Since it is difficult to carry out classification in such a fine region by a dry method, it is carried out by a wet method. The liquid to be dispersed (referred to as a dispersant) is water, alcohol or the like. Since the particles need to be charged for stable dispersion, highly polar water is desirable. The substance added to charge the particles and make a stable slurry is called a peptizer. Acrylate or phosphate is used as the peptizer. If necessary, adjust the pH to a range within which the slurry is stable. Usually, the powder is dispersed in an aqueous solution in which the peptizer is dissolved in an amount of 0.2 to 0.5% by weight. A solution in which the powder is dispersed is treated with a ball mill in order to grind large particles and disperse secondary particles. The ball mill is preferably made of a silicon nitride sintered body in order to prevent contamination of impurities.

When the slurry is left to stand, large particles settle quickly. This is called spontaneous sedimentation, and the particle size that sinks at a certain height for a certain period of time can be easily calculated. This phenomenon is also used as a method for measuring particle size distribution. Therefore, it can be guaranteed that, after a certain period of time, there are no particles larger than some particles in the upper liquid. The problem here is 0.5
Natural sedimentation takes a long time to remove particles larger than micron. Therefore, a centrifugal separation method using a centrifugal separator is desirable. When the supernatant liquid in which only fine particles are dispersed is diluted and the particle size distribution is measured, the relationship between the sedimentation conditions and the particle size to be removed can be solved.

Particles containing almost no particles of 0.5 microns or more can be prepared by such a method. When the particle size distribution of this powder is measured, for example, a small amount of particles exceeding 0.5 micron are observed as in Example 3 of FIG. When this specific surface area is measured by the nitrogen adsorption method, it is 31.5 m ² / g, which is several times the value calculated from the particle size distribution. Also, no large particles are observed using an electron microscope. From these facts, the large particle size measured is presumed to be the weakly bonded secondary particles in which the dispersed particles are recombined. In fact, even if an oxide was added to this powder as a sintering aid and sintered at 1800 ° C. for a long time, a sintered body composed of uniform and fine particles was obtained, and no columnar particles were observed. Therefore, this powder has a uniform particle size without the core of columnar particles.

As a result, it became clear that the average particle size is preferably in the range of 0.1 to 0.35 micron. However, if it is larger than 0.35 micron, there is always a large particle serving as a nucleus of grain growth. If it is smaller than 0.1 micron, the chemical reactivity of the powder becomes high and oxidation progresses during the treatment,
Moreover, it is not suitable for sintering because it is difficult to densely fill the powder. Therefore, the specific surface area of the powder is 15 to 50 m ² / g. It is preferably in the range of ²⁰ to 35 m ² / g.

When the average particle diameter is within the above-mentioned predetermined range and the specific surface area is less than 15 m ² / g, there is a high possibility that large particles or secondary particles having strong bonding remain. on the other hand,
The average particle size is within the above range and the specific surface area is 5
When the average particle size is larger than 0 m ² / g, the same problem occurs as when the average particle size is smaller than 0.1 micron. If the average particle size and the specific surface area are within the above ranges, the α / β ratio in the powder may be basically arbitrary. However, when α and β are mixed, the phase transition occurs non-uniformly during sintering, and it is not easy to control the structure. Therefore,
A single phase containing 80% by weight or more of α phase or β phase or a powder close to it is desirable.

The powder satisfying the above-mentioned average particle size and specific surface area can be used as a raw material for a sintered body by itself, and can also be used as a mixture by adding a powder having another particle size distribution to this powder. it can.

For example, in a fine powder satisfying the above average particle diameter and specific surface area, the average particle diameter exceeds 0.5 micron and 1.
When a powder having a size of 5 microns or less (preferably 0.7 to 1.0 micron) is mixed as a nucleus, only large particles grow in a columnar shape. If the average particle size of the latter particles is within this range, and the particles within this range account for 70% by volume of the total, the function as a core is sufficiently achieved. If it is smaller than this range, the difference from the matrix is small and selective growth does not always occur. If it exceeds this range, the grown columnar particles are too large and the strength of the sintered body is reduced. Since this particle acts as a nucleus, it needs to be a single particle. Therefore, the specific surface area needs to be 5 m ² / g or less. Even if this powder is added in an amount of 0.05 to 5% by weight with respect to the above-mentioned fine powder and sintered, the amount is small and excellent sintering characteristics are maintained. Further, as the sintering progresses, nuclei grow as columnar particles and a composite structure is developed. However, if it is less than the above-mentioned predetermined amount, the action as a nucleus is not sufficient, and if it is more than 5% by weight, the number of nuclei is too large and the columnar particles come into contact with each other to act as a large defect to reduce the strength. And shows a large intensity distribution. It is preferably in the range of 0.5 to 2% by weight. In order for the added powder particles to act as nuclei, β that is stable at high temperature
It must be a mold, and its content is 80% by weight or more.

[0026]

EXAMPLES The present invention will be described more specifically with reference to Examples and Comparative Examples of the present invention.

[0027]

[Examples 1 to 3],

Comparative Examples 1 to 3 Silicon nitride powder commercially available as a sintering raw material (A: SN-E10 manufactured by Ube Industries, B: SN-P21EC manufactured by Denki Kagaku Kogyo Co., Ltd., C: SN- manufactured by Denki Kagaku Kogyo Co., Ltd.) P21FC) For each 20 g, the slurry concentration is 10
An aqueous solution of sodium hexametaphosphate having a concentration of 0.3% by weight was added so that the concentration became 0.3% by weight, and wet mixing and dispersion were performed for 3 hours in a ball mill made of silicon nitride to prepare a silicon nitride powder slurry.

Next, this slurry was centrifuged with a centrifuge.
After treating for 5 minutes under the condition of 00G, 150 cc of the supernatant silicon nitride fine powder slurry was recovered. In addition, the sediment obtained by centrifugation is an aqueous solution of sodium hexametaphosphate 15
After adding 0 cc and redispersing for 10 minutes with a homogenizer having an output of 400 W, centrifugation was performed for 5 minutes under the condition of centrifugal force of 1400 G. Repeating these dispersion-classification operations four times,
A total of 750 cc of silicon nitride fine powder slurry was prepared.
Next, this silicon nitride fine powder slurry was subjected to a centrifugal force of 140
Centrifugation was performed again at 0 G to improve the classification accuracy. The obtained silicon nitride fine powder slurry was subjected to centrifugal force 16 to remove sodium hexametaphosphate added as a dispersant.
The mixture was centrifuged at 00 G for 1 hour to remove the supernatant, distilled water was added, and the mixture was dispersed for 10 minutes with a homogenizer having an output of 400 W to obtain a silicon nitride fine powder slurry again. After performing such washing operation three times, the obtained silicon nitride fine powder slurry was dried to prepare silicon nitride fine powder. For comparison, the results obtained by ultrasonically dispersing the powders of Examples 1 to 3 in an aqueous sodium hexametaphosphate solution were set as Comparative Examples 1 to 3, respectively.

In FIG. 1, the particle size distribution was measured by diluting the silicon nitride powder slurry dispersed in the sodium hexametaphosphate aqueous solution obtained during the above operation (Example 3), and Comparative Example 3
It shows in comparison with the result of. Laser scattering method (N
& L company particle size distribution meter "Microtrac-SPA"). Table 1 shows the powder characteristics of the silicon nitride powders of Examples 1 to 3 and Comparative Examples 1 to 3.

The physical properties shown in Table 1 were measured as follows. α phase content (%): According to the powder X-ray diffraction method,
It was calculated from the intensity ratio of the (10) plane and the (210) plane of the β phase. Oxygen amount (wt%): LECO O / N analyzer "TC-1"
36 ". Specific surface area (m ² / g): Canter Soap Jr. manufactured by Yuasa Ionics Co., Ltd. It was based on the BET one-point method.

As a result, as is clear from Table 1, the powders of Examples 1 to 3 have a smaller average particle size and a larger specific surface area than those of Comparative Examples 1 to 3. .

Next, 93% by weight of each of the silicon nitride powders of Examples 1 to 3 and Comparative Examples 1 to _{3 was} added with 5% by weight of Y ₂ O ₃ (fine powder manufactured by Shin-Etsu Chemical Co., Ltd.) and MgO (Wako Pure Chemical Industries, Ltd.). 2% by weight of special grade reagent manufactured by, made by wet mixing in hexane for 3 hours, dried and then crushed.

Next, about 2 g of these mixed powders was filled in a carbon die having a diameter of 15 mm coated with boron nitride powder, and under a nitrogen atmosphere, a pressing pressure of 20 MPa and a heating rate of 3
Under the condition of 0 ° C./min, the temperature was raised to a temperature at which the density of the sintered body was 90% or more, and hot press sintering was performed in a rapid cooling pattern to compare the sinterability and prepare a silicon nitride sintered body. . The density of the obtained sintered body was measured by the Archimedes method. Scanning electron microscope (SEM)
Was used to examine the homogeneity of the fine structure. Table 2 shows the relative density of the obtained silicon nitride sintered body.

From the results shown in Table 2, the powders of the respective examples were superior to the powders of the comparative examples in sinterability and reached a high density at low temperature. The sintered body structure was a very fine and uniform sintered body structure containing no coarse particles.

[0035]

[Table 1]

[0036]

[Table 2]

[0037]

[Examples 4 and 5],

[Comparative Example 4] Al ₂ O ₃ (AKP-2 manufactured by Sumitomo Chemical Co., Ltd.) was added to 93% by weight of each of the silicon nitride fine powders of Examples 1 and 3 and Comparative Example 1.
0) wt%, Y ₂ O ₃ (Shin-Etsu Chemical Co., Ltd. fine powder) 4 wt%
Was added, wet-mixed in hexane for 3 hours and dried,
It was crushed.

Next, these powders were molded into a mold at a pressure of 100 kg / cm ² and then subjected to hydrostatic pressure (C) at a pressure of 3 tons / mm ^2.
IP) was molded. The obtained CIP compact was set in a carbon crucible together with a stuffing consisting of silicon nitride powder and BN powder, and was placed in a nitrogen atmosphere of 1 MPa at a temperature of 175.
Gas pressure sintering was performed at 0 ° C. for 2 hours to prepare a sintered body.

The density of the obtained sintered body was measured by the Archimedes method, and then cut and mirror-polished.
The polished surface is plasma-etched and scanning electron microscope (S
The structure of the sintered body was observed by EM). Table 3 shows the relative density of the obtained silicon nitride sintered body.

As is clear from Table 3, each of the powders of Examples 4 and 5 has a relative density of 99% or more, and is superior in sinterability as compared with Comparative Example 4, and the sintered body structure thereof is The structure was a fine and uniform sintered body that did not contain β-columnar particles with abnormal grain growth.

[0041]

[Table 3]

[0042]

[Example 6] In Example 3, 300 cc of the sediment remaining after 5 times of centrifugation was transferred to a beaker, 250 cc of an aqueous solution of sodium hexametaphosphate was added, and an output of 40
A 0 W homogenizer was used for dispersion for 10 minutes to prepare a silicon nitride powder slurry. The slurry was allowed to stand for 20 hours to spontaneously settle, and 200 cc of the supernatant was removed. The above redispersion-sedimentation classification treatment was repeated 10 times. Then, 200 cc of distilled water was added and dispersed by a homogenizer, and again classified by natural sedimentation for 20 hours to remove sodium hexametaphosphate added as a dispersant. After performing such a washing operation three times, it was dried to prepare a silicon nitride powder D shown in Table 4. The particle size distribution of this powder is shown in FIG.

Next, the silicon nitride fine powder of Example 3 9 l.
5% by weight, 1.5% by weight of silicon nitride powder D, Al ₂ O ₃
(AKP-20 manufactured by Sumitomo Chemical Co., Ltd.) 3% by weight and Y ₂ O ₃ (fine powder manufactured by Shin-Etsu Chemical Co., Ltd.) 4% by weight were added, and 3% in hexane was added.
After wet-mixing for an hour and drying, it was crushed. This mixed powder was sintered in the same manner as in Example 4 to prepare a silicon nitride sintered body.

The relative density of the obtained sintered body was 98.9%.
The structure of the sintered body was a composite structure composed of fine matrix particles and grown β-columnar particles. 10
Press the diamond (Vikars) indenter with a pressure of kg,
Fracture toughness value measured from the length of the generated crack is 8.2MPa

[Equation 1] Then, the value of the sintered body of Example 3 in Table 2 in which nuclei were not introduced (4.2
MPa

[Equation 2] ) It has higher toughness.

As described above, it became possible to produce a sintered body having a composite structure by developing columnar particles from the nucleus by using the powder which gives a matrix of uniform structure.

[0046]

[Table 4]

[0047]

As described in detail above, according to the present invention,
An average particle size within the range of 0.1 to 0.35 microns, and
A fine and uniform particle size of silicon nitride fine powder having a specific surface area of 15 to 50 m ² / g is obtained. By using this powder, it is possible to sinter at a lower temperature than that which is commercially available, and the structure of the sintered body is fine and uniform. Also, if coarse particles mainly composed of β-type having an average particle size of more than 0.5 micron and 1.5 micron or less and a specific surface area of 5 m ² / g or less are added to this fine powder as a core, From this, columnar particles develop and a sintered body having a composite structure can be manufactured.

[Brief description of drawings]

FIG. 1 is a diagram showing a result of particle size distribution measurement by a laser scattering method.

Claims (5)

(57) [Claims] 1. An average particle diameter measured by a laser scattering method is in the range of 0.1 to 0.35 micron, and the particle diameter is 0.3.
The content of particles of 5 microns or more is 15% by volume or less, the content of particles of particle size of 1.0 micron or more is 3% by volume or less, and the specific surface area is in the range of 15 to 50 m ² / g. A crystalline silicon nitride fine powder characterized by: 2. The silicon nitride fine powder according to claim 1, wherein the β phase content is 80% by weight or more. 3. The silicon nitride fine powder according to claim 1, wherein the α phase content is 80% by weight or more. 4. A ball mill is used to wet-disperse silicon nitride powder in a solvent to form a silicon nitride powder slurry, and coarse particles are removed by wet sedimentation classification to produce fine particles having a narrow particle size distribution. The method for producing a silicon nitride fine powder according to claim 1, wherein. 5. The average particle size measured by a laser scattering method is more than 0.5 micron and 1.5 micron or less, the particles within the range are 70% by volume or more of the whole, and the specific surface area is 5 m ² / Silicon nitride powder having a β phase content of 80% by weight or more and a g content of 0.1 to 5% by weight with respect to the silicon nitride fine powder according to claim 1. Fine powder.